Linear magnetic brake with two windings



SR GROSS HU'LNLNUE, MF- V" INVENTORS HEINRICH G. KOSMAHL ATTORNEYS H. G. KOSMAHL LINEAR MAGNETIC BRAKE WITH TWO WINDINGS Filed Dec. 12, 1966 Patented Feb. 3, 1970 LINEAR 3 ABSTRACT OF THE DiscLosURE,

Linear}; magnetic braking using a pair of inductively coupled circuits. A primary coil is r' onunit'ormly wrapped about a gtubular core with a winding density which produces a'ponstant force on a secondary coil.

ORIGIN OF THE INyENTION The invention described herein was made by an employee ofthe United States Government and may be manufactured and used by or for the Government for governmental [purposes without the thereonior therefor.

gAcKGRoUND OF THE; INVENTION This invention is concerned with the controlled deceleration o t'. fa moving mass. The invention is particularly directedjto an improved magnetic brake system for stopping a falling body.

A controlled stopping of a falling mass presents some diflicult braking problems. In many applications the rate of deceleration must not exceed a -yery low maximum to avoid damage to the payload. Also, the amount of energy which can be expended in decelerating the Object should be keptltb a minimum.

Thesg', problems encountered in decelerating a moving body have been solved by a magnetic brake system constructedsin accordance with the -present invention. The mechanism of operation of this system is based on Lenzs law states that magnetic fields induced in one circuit as-.a .result of interaction withQanother circuit oppose each other. This system relies on the mutual inductance betweengtwo magnetically coupled and unconventionally wound Lc ircuits spaced from one another. One of thes circuits lhas a primary magnetic coil whose configuration is such that the motion of a secondary magnetic coil throughfthe fields of the primaryfioil is brought to a stop under controlled conditions requiring'minirnum primary energy? f I It isf therefore, an object of the present invention to provideaj magnetic brake system which will bring a known mass to af full stop with a minimum: expenditure of energy.

A fll l'fllel' object of the inventioig is to provide a magnetic h rjgike system in which the; braking action is accomplisfisd in a precisely adjustable manner with respect to the desired degree of deceleration by simply varying the voltage and current of a primary circuit.

These and other objects of the invention will be apparent rom the specification which follows and from the drawing in which like numerals are used throughout to identify like parts.

Tlfe drawing is a schematic illustration of a magnetic braking system constructed in accordance with the present invention.

Referring now to the drawing, the braking system utilizes a pair of magnetic coils 1 and 2. The primary coil 1 is fixed in a desired position, such" as at the bottom of a drop tower in a zero gravity research facility. The secondary coil 2 forms a part of a movable structure, such as a drop tower experiment capsule 8 Claims payment of any royalties 7 of movement The coil 1 comprises a conductor 10 having a large diameter d, which is wrapped about a hollow tubular core 14 as shown in the drawing. The coil 1 has one'of seve'ifal configurations which will be described later in greater detail. The coil 2 likewise comprises a large diameter conductor 12 which is'uniformly wrapped about a cylindrical core 16,-}; and the ends of the-conductor 12 are short circuited by a-line 18. Y

A payload 2 0 is rigidly mounted on one end of the coil 2 and is preferably magnetically noninteractive. The coil 2, core 16 and payload 20 comprise a test package -'22 which is free 'to fall towards the fixed primary coil 1. in the direction of the arrow shown in the drawing. The path bf this test package 22 is along the axis of the tubular colic 14.

The interaction of the two coils 1 and 2 can best be described by 'their mutual inductance M in henries. The primary coil is connected to a power source 24 which provides a load voltage V in volts and has an impedance R in ohms which is much smaller than the impedance R of the cdilj 1. The bottom end 26 of the coil 1 away from the coil '2 represents the origin of a coordinate system in which fthe axial coordinate is z. The test packa 22 moves only in the z direction.

The payload 20 has a given mass m, while the coil 2 together with its core 16 have a mass m,. The total mass m in kilograms of the test package 22 is m +m Prior to any interaction between the primary coil 1 and secondary coil} 2 a steady-state current i from the power source 24 flows in the conductor 10. As the test package 22 moves in the z direction its momentary distance from the bottom end 26 of the coil 1 is z. The instantanepus velocity 'z[z(t)1] of the coil 2, where z is the first derivative, is determined from the following equations in which L is the selt inductance in henries of the coil 1 and i v is the current flow in the second coil 2 in kiloamperes.

The repelling magnetic force F acting upon the turns 12 of the falling payload is where z is the distance between defined points in coils 1 and 2. In the following equation of motion of the pay load 2 is the second derivative and the value of g is 9,81 meters per second per second.

since '2 (0), the velocity at z=h, is zero.

The initial value conditions are 11(0) =1}, and i =0. After M=M(z) has been computed, Equations 1, 2 and 5 are solved simultapeously for z(t) and z(t). The

values z(t,)=0 and :03) give the stopping time t, and stopping position z(t,)=x of the payload above the ground level. a

It is evident from these equations that the stopping lcation u'ces sub f d,=0.l t decreases d from ires time constant 1- be as small as possible where the magnetic field is unconstrained in order for the current to time t which is less'=thari or equal to approximately twice the free fall time through a height h. By way of example,

1s increase 0.75 to 1.0 meter and the primary coil radius is 1.5 meters.

bout a full stop In addition to the aforementioned geometrical parameters these two tables contain the primary coil voltage 4 build up as close' to itsfinal value i as possible in a where h=l meters the time t: 10 seconds is the max mum period available for the build up of current in case 1 t' forc ersists even after 2 has reached of a two'way Pj Y expeflmem' The dece era mg 6 p zLz/Rz Ofthe Secondary Other conditions for experiments conducted} in the coil 2 prevents an instantaneous decay of i to zero. g zgl ggzgn 3132:3112: 3%"g s ih ggzvg gggiiefigt z bring the payload 22 to a full stop can be reduced substantially if the condition G is equal to or less than 30 is Also listed in Tables I and 2 are two values of the g fi ggs g ggfiz i zgfi action can be accomplished for alummum Whlch are A study of Tables 1 and 2 indicates that the appl 3 10 (Sz)(m) of cryogenic cooling to the secondary turns red O stantially the primary power requirements in th at room temperature T=300 K and 06x10 (0) (m) v at T=80 K. The primary current i is not absolutely fig g' i sf f g gg :21 2 gg sz constant; however, because of the relatlvely large time. p a he s-bfindafy c1331 mdiug n constant T the current i changes by less than ten pery cent of the initial i value, 1

The parameters shown in Tables 1 and 2 are app ica- I ble to a payload 20 having a mass m oi900 kilograms 2: equal I g Z re'slsuvmg f g g to which the mass of an aluminum conductor 12 has been ame T, co f 8 P 5 3" an Ta added. The diameter of the primary coil is three meters. the ndary c0112 while-keeping G equal to F The primary turns consist of 0.1 meter diameter copper the power r qu me t f the three t ulat d wmdwire 10 having a specific resistivity p of 1.8 10- ohms mg configurations necessary to bring a meter, are approximately the same. However, the energy re- Parameters for three difierent winding configurations quirements are not equal. of the primary coil 1 are set out in Tables 1 and 2. The The primary coil configuration having a winding denprimary coil 1 of the system described in Table 1 has a sity w =c0nstant x[l(z/l)] produces the shortest time Winding dwsity 0f U-1 1) The first S X va u s listed constant r =2.3 seconds. This configuration also requ a e r. 0 e hww mwmwm nf r e T e W W 6 m. S. r. t; V m n a H. O O .1 c n steam W P .m mu ar mmr s m y me a e 0 m s s seamsms w ehmeeemmm mid m s c P 4s a e aew 2 2 aaaaaaaasa t a I h adm .B n u r m .n m, hT m mm mi e asnanssesa w umsmmmmms m m m m m n e w musuamammmmnnuwmm rzmiiimn c v. ai P h 1 r1 0 p 1 A s Pfid o M 8 5 fi e! I .r... 50 0879869 3 m 3 .5 a sm ua s tutti. im m i o u c m n .m. a 22L LLa ttla S. .1 O 1 e bl m m m .2 m 8 2 6.0 7.8..800285682 8 n- 30 0 0 6 7 6-3 S J... u L9. 4 m 2 m .m n emm ammw.aaaaawammamam a snnwammmam when wa m r. b g w mw w 2 d T M h m t V N .8 302700027000000 m O M MMM n k & aom L& 1 39 m gi w .m m m m s. pmmmmmmmmnmmwmnnmm m nm u win 1 .1 a .nl.t Trh m P 78 8651 507 V 0 1715 21 .m m w m m m mm m mmwnmnmmnammmm munwamnmam 0 5 m 6 66078802666222 m .mfifi fi fiw fi fi WM l b" 0 0 0 00 LLL L111 2 In. 0000000 f t .l U C W U m S a E E g s f e L L an H2 g hwm w B m mmmfimmfifififififififififififi B m m m m 28%3 M LLL M 0000000 C m m m m m m 6 Z 3 l 6 m m 66.066666666662468 m 66 6666666 h a m 2 S C n r. O l 1 l t S d T. S S D e 6 B W a C n n m mmmmfl meww m m .1 a t S a t m rl mmov w a r n m n m w n a .l d a .1 e 2 t 0 m V n nvm m 1m T C 0660000000600000 m w0 6 0 6 m600 Y w m r nm 3 3 33 0 .W m m 6 w 6 0 6 uh T g m C rx 3 0 0 3d 0 S S h H a n r m m 6 0 h S 0 t 1 n a Y n r f m mn ae A l a r mew 2 cm Pb m mwmewmw e cl 0 lu e S S r t e 0 e C 0 md m u 2 am. b Mb 6 C Y n .l d n g t p l C a u d .mu me. v, n c d g 5 'm w 0d n r an ssen m .EWOS ME Dfimm MM Ck d m C r n C m 0 um malmmmw mf. t a m m e m w mn 0 e S S .T. p S e W r. S E t. 8 m m m n m S 1 Q s o m Cfi mmcduu .ww m m V the steady-state primary current i at the beginning of interaction, the power P, the normalized force G in multiples of go, and the position x at which the center of the payload turns approaches zero velocity, measured from the bottom end 26 of the primary coil where 1:0.

zero because the time constant 1 Therefore, the repelling magnetic force F remains finite over a period of a few constants, and a perfect stop is possible.

specific resistivity p the smallest number of turns to bring about a full stop of the payload.

The meaning of the term full stop refers to a motion in which the velocity decays directly to zero without oscillations in the sign of the deceleration. That is, there is no acceleration. The position of the stop in all symmetrically wound coils lies above the coil center where z=l /2. This occurs because in symmetric coils the mutual inductance M has a maximum and dM dz at the center of the coil. Thus dM/dz reverses its sign in going through the center. In the expression for the repelling force F set forth above in Equation 3, i (t) remains almost constant and the sign of i depends primarily on that of dM/dz. Because the time constant T; is

rarely below 0.1 second a reversal in the sign of dM/ dz in going through the center would preclude that occurring in i Therefore, if the payload 20 moves over the center, a short period of acceleration will follow: the payload velocity would increase temporarily before final deceleration could occur to cause the final stop. This two phase deceleration with a short acceleration period in between produces a workable mode of operation requiring approximately percent less power than one phase stop ping.

The eifect of changin 1 on the power requirement indicates an optimum length is less than This is be cause two competing factors produce a minimum power requirement. More particularly, increasing increases the flux through the secondary coil which increases the braking force. However, the mass m increases proper tionally with and reduced the elfect of the decelerating force in front of the integral in Equation 5.

A clear dip in power requirements occurs when the winding density of the secondary coil W is changed as shown in Table 1. This optimum occurs because of the competing effects between the secondary time constant 1 which prevents a rapid build-up of i and the mutual inductance M Because both T2 as well as M increase with increasing W2, a minimum in the required power occurs if the total interaction timeis not substantially larger than 1 Although several embodiments of a braking system constructed in accordance with the invention have been described, it will be appreciated that various structural modifications may be made without departing from the spirit of the invention or the scope of the subjoined claims. For example, the payload 20 in the system described is magnetically noninteractive. However, it is contemplated that certain installations may have pay loads that are magnetically interactive with the primary coil. It is further contemplated that the magnetic field may be constrained to the inside of the tubular core by placing a magnetically conducting membrane perpen-= dicular to its axis. With such a modification the time constant T1 is of little importance, and the field can be built up prior to the ejection of the payload.

What is claimed is:

1. Apparatus for stopping a freely falling body with a minimum expenditure of electrical energy and a predetermined amount of deceleration comprising a tubular core being rigidly mounted in the path of the freely falling body and having a diameter greater than said body to enable the same to enter said core,

a first constant diameter conductor forming a single primary coil wrapped about said tubular core,

a power supply connected to said primary coil for passing a predetermined current through said primary coil to create a first magnetic field therein,

a cylindrical core mounted on the freely falling body,

a second constant diameter conductor forming a secondary coil wrapped about said cylindrical core, and

means for short circuiting the ends of said secondary coil to enable an induced current to flow therein as said secondary coil moves through the magnetic field of said primary coil thereby creating a second magnetic field in opposition to said first magnetic field,

said primary coil being nonuniformly wrapped with a winding which produces a constant force.

2. Apparatus as claimed in claim 1 wheren the primary coil has a winding density of K (l-z/l) where K is a constant, z is the distance from one end of the coil and l is the length of the coil.

3. Apparatus as claimed in claim 1 wherein the decele ration is smaller than 30 gs and the primary coil has a winding density of 10 (l-z/l) where z is the distance from one end of the coil and l is the length of the coil.

4. Apparatus as claimed in claim 1 wherein the secondary coil is uniformly wrapped about the cylindrical core.

5. Apparatus as claimed in claim 1 wherein the primary coil is mounted at the bottom of a drop tower in a zero gravity research facility, and the moving body comprises a drop tower experiment capsule.

6. Apparatus as claimed in claim 5 wherein the drop tower experiment capsule is free to fall toward the pri mary coil from a predetermined height.

7. Apparatus as claimed in claim 5 wherein the drop tower experiment capsule includes the secondary coil, the cylindrical core within said secondary coil, and a payload rigidly mounted ,on one end of said core.

8. Apparatus as claimed in claim 7 wherein the payload is magnetically noninteractive.

References Cited UNITED STATES PATENTS 1,873,122 8/1932 Hartzell 336-224 XR. 1,985,254 12/1934 Huse 310l3 1,989,205 1/1935 Loughlin e.- 336224 XR 3,260,870 7/ 1966 Beach 310-14 3,300,744 ,1/ 1967 Deutsch 310-14 ORIS L. RADER, Primary Examiner A. G. COLLINS, Assistant Examiner U-S- 1. X-R. 

